1. Field of the Invention
This invention relates to a process for improving the mechanical properties of metals, and more particularly to a process for producing an aluminum composite having a rapidly solidified metal matrix and a continuous fiber reinforcement.
2. Description of the Prior Art
An aluminum based composite generally comprises two components--an aluminum alloy matrix and a hard reinforcing second phase. The reinforcing phase may be discontinuous, e.g., particulate, short fiber, or may be continuous in the form of a fiber or tape. The composite typically exhibits at least one characteristic reflective of each component. For example, a continuous fiber reinforced aluminum based composite should reflect the ductility and fracture toughness of the aluminum matrix as well as reflect of the elastic modulus and strength of the fiber.
Continuous fiber reinforced aluminum based composites are usually limited to ambient temperature applications because of the large mismatch in higher temperature strength between the aluminum matrix (low strength) and the continuous fiber reinforcement (high strength). Another problem with continuous fiber reinforced metal matrix composites produced by mechanically binding continuous fiber between aluminum based matrix foils is the difficulty in producing a bond between the matrix and the fiber. To produce such a bond it is often times necessary to vacuum hot press the material at temperatures higher than the incipient melting temperature of the matrix or higher than the stability of precipitate phases present in the aluminum based matrix. Still another problem with continuous fiber reinforced metal matrix composites produced by cold spraying a rapidly solidified aluminum based matrix mixed with an organic binder onto a continuous fiber preform and then burning off the organic binder is that the organic binder decomposes and forms a deleterious residue within the sprayed preform. An alternative method of fabricating the composites is by plasma spraying. Prior processes in which alloys and/or continuous fiber reinforced metal matrix composites are fabricated by means of plasma or arc spraying are disclosed in U.S. Patent Nos. 3,596,344, 3,606,667, 3,615,277, 4,782,884, 4,786,566, and 4,805,833. However, all the previous work was done using atomized aluminum powder which did not have the metastable microstructure of rapidly solidified aluminum powder. Hence, there is a need for an invention for plasma spraying a rapidly solidified aluminum alloy matrix where rapid enough solidification of the molten powder droplets be attained to retain the microstructure of the starting rapidly solidified alloy.